Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$170.86	8.572%	$185.5061	$185.51	$185.50	$185.50
Purchase #2	$102.78	7.861%	$110.8595	$110.86	$110.85	$110.90
Purchase #3	$246.75	13.261%	$279.4715	$279.47	$279.45	$279.50
Purchase #4	$228.94	12.285%	$257.0653	$257.07	$257.05	$257.10
Purchase #5	$109.43	6.362%	$116.3919	$116.39	$116.40	$116.40
Purchase #6	$83.33	8.411%	$90.3389	$90.34	$90.35	$90.30
Purchase #7	$84.99	8.277%	$92.0246	$92.02	$92.00	$92.00
7 purchase totals =	$1,027.08		$1,131.6578	$1,131.66	$1,131.60	$1,131.70